Ground source heat pump system for geothermal development and utilization
1. Introduction
The intelligent drilling equipment manufacturing base project of Xi'an Research Institute covers an area of about 190126,667 m2, with a planned total construction area of about 109805.64m2, an above-ground construction area of about 97973.66 m2 and an underground construction area of 11831.98 m2. Main structures: complex building, drilling rig workshop (No.2 workshop), joint station building, equipment ex-factory inspection workshop, drilling tool production workshop, bit production workshop, etc. Ground source heat pump technology is used in the whole plant area to provide cooling, heating and domestic hot water in indoor areas.
2. Solution
The designed cooling load and heat load of the project are 4200kW and 2700 kW, and the unbalanced rate of heat release in summer and heat removal in winter is 1.21. Considering the intermittent heat release mode and underground seepage during the operation period, it is beneficial to the recovery of soil temperature after operation, and through real-time monitoring and optimized operation, the balance between the cold and the heat of soil source can be ensured. Using indoor test and field thermal response comprehensive test, the geotechnical thermo physical parameters were obtained, which accurately guided the design.
The comprehensive energy efficiency of ground source heat pump system was evaluated on the basis of the indoor application effect, heat pump unit performance, transmission system performance and characteristics on soil source side.
3. Construction Situation
Figure 3-1 Outdoor rending of No.2 Workshop
The work quantities of the project mainly include 504-opening outdoor heat exchange holes, horizontal pipeline gathering and transmission system, ground source heat pump unit system room and building terminal, and 504-opening heat exchange wells (double U-shaped DN25PE100 1.6MPa pipes) arranged on the east, south and west sides of No.2 workshop, with effective hole depth of 150m and aperture of 150mm.
Figure 3-2 Layout plan of ground source heat pump project in No.2 Workshop
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Figure 3-3 Laying works of horizontal Pipes | Figure 3-4 Quality inspection in construction Process |
4. Achieved Accomplishment
This project has operated for a complete cooling season and heating season, with a good effect. In summer, the outlet water temperature of buried pipe in stable period is 22.4 ~ 25.0°C, the temperature difference is between 3.2 ~ 5.6°C, the flow rate of buried pipe system is 900m3/h, and the maximum cooling load of ground source heat pump system is 4219kW. In winter, the outlet water temperature of the buried pipe is 14.2 ~ 15.8°C, and the temperature difference is between 3.0 ~ 4.1°C. The maximum heat load of the ground source heat pump system is 4104kW, which meets the design requirements.
In summer, the indoor temperature of the user-side office area is between 19 ~ 23°C and the humidity is between 39% and 55%, and the temperature of the industrial building is between 22 ~ 25°C and the humidity is between 32% and 57%. In winter, the indoor temperature of the user side office area is between 19 and 24°C, and the humidity is between 34% and 65%; the temperature of the industrial workshop is between 17°C and 19°C, and the humidity is between 32% and 57%. This meets the needs of users and achieves a good effect.
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Figure 4-1 Machines and pipelines in the machine room | Figure 4-2 Refrigeration operation conditions in summer | |
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Figure 4-3 Operating conditions of heating in winter | Figure 4-4 Indoor temperature on user’s side in summer and winter | |
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Figure 4-5 Test of heat exchange characteristics of buried pipes | Figure 4-6 Automatic monitoring station for temperature stress field of Buried pipes |
5. FAQ
Q1: How long is the service life of ground source heat pump and how long is the payback period?
The underground heat exchanger of this project is made of 1.6MPa HDPE, which has a very stable material performance, strong corrosion resistance and excellent tensile and fracture resistance. The service life of the heat exchanger will be more than 50 years, almost the same as that of buildings. The static payback period of this project is 8.9 years.
Q2: How to balance the soil temperature field?
In this project, through the design of cooling load and heating load, the heat release in summer is basically balanced with that in winter. Meanwhile, through the monitoring data of temperature field in different regions, the heat exchange parameters of the system are adjusted at proper time, and the temperature recovery period after the end of a cooling season and a heating season is assessed, which provides a basis for the later operation.
Q3: What is the energy saving effect of the project?
COP (coefficient of performance of air conditioner) is taken as 5.0, and EER (energy efficiency of refrigeration of air conditioner) is taken as 5.8 for ground source heat pump system in this project, much higher than 3.0 of ordinary air conditioner, indicating a higher energy efficiency than ordinary air conditioner. At the same time, the ground source heat pump system does not need to consume fuel when heating, which plays a very good role in pollution control and haze reduction. It saves 100,000 cubic meters of gas and 330,000 kWh of electricity every year, and there is no emission of waste gas, waste residue and wastewater.
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